1. Field of the Invention
The present invention relates to a data I/O system and a method of controlling the data I/O system, and specifically relates to a technology to ensure availability of a secondary mirror volume in which a copy of data of a primary volume is written.
2. Description of the Related Art
Recently, storage systems that manage rapidly increasing data assets have played a vital role in an enterprise information infrastructure. In an increasing social demand for the storage like this, the storage system requires very high availability such that 24-hour-a-day, 365-day-a-year nonstop safety operations are possible. Therefore, the recent storage systems have adopted various technologies to improve the availability of the main transaction processing, such as a mechanism to backup data and a mechanism (replication) to copy data for data analysis or development/testing with no impact on main transaction processing (for example, see U.S. Pat. No. 6,101,497). In the above replication, data stored in a volume (primary volume) applied to main transaction processing is copied to another volume (secondary mirror volume), and this secondary mirror volume is used in various secondary transaction processing such as data backup, data analysis, and development/testing. Thus, it is possible to minimize the influence of the secondary transaction processing on the main transaction processing, which also improves the availability of the main transaction processing.
The aforementioned replication technology can basically improve the availability of the primary volume used in the main transaction processing but does not take into consideration availability of the secondary mirror volume. However, actual transaction processing often requires the availability of the secondary mirror volume used in the secondary transaction processing. For example, a content of the secondary mirror volume is sometimes corrupted by a bug inherent in a program, a hardware error, and the like in the transaction processing such as data analysis and development/testing. In such a case, a mechanism is required to simply and quickly recover the secondary mirror volume. In recovery of the secondary mirror volume, the content of the secondary mirror volume is not always restored to an expected content even if data of the primary volume is copied to the secondary mirror volume. The content of the primary volume at the time of copying could have been already updated, and the content after restored does not always agree with the content of the secondary mirror volume before corrupted.